In a typical prior art vane-type cam phaser, a controllably selective locking pin is slidingly disposed in a bore in a rotor vane to permit rotational locking of the rotor to the stator (or sprocket wheel or pulley) under certain conditions of operation of the phaser and engine. In ILP camshaft phasers, the rotor is lockable to the stator at an intermediate position in an increased rotor range of rotational authority. The position of the rotor is governed by application of pressurized oil to one side or the other of the rotor vanes via an oil control valve (OCV). The timing of engine combustion valve events can be varied continuously by controlling oil pressure through the OCV to the cam phaser attached to the camshaft. In one type of ILP camshaft phasers, a separate oil ILP control valve is used to control oil flow to the ILP locking pin with a separate command from the ECU.
The addition of an intermediate locking pin and accompanying ILP control valve introduces new control requirements for an engine management system (EMS). The present invention relates to a specific control method and diagnostic for ILP cam phasing. The invention comprises a strategy for controlling the OCV and ILP duty cycles together so that the cam phaser is operated and diagnosed correctly at all engine operating conditions.
What is needed in the art is a method and diagnostic for ILP camshaft phasing.
It is a principal object of the present invention to improve the operation and reliability of an ILP camshaft phaser.